The invention relates to an assembly comprising a first element to which a second element is secured by means of an adhesive.
European Patent Application No. 0,090,218 discloses an optical assembly with an optical component with two divider prisms and a part of an apparatus, an adhesive being applied in the gap between the optical component and the part.
In optical assemblies used in optical apparatus such as optical-disc players it is important that the various optical elements therein are positioned correctly relative to one another. For production reasons it is therefore essential that the optical elements in such assemblies are disposed at the correct predetermined location and in the correct position relative to, for example, a reference plane. Important in this respect is the positional accuracy in the direction of the optical axis (Z-direction) of the optical assembly, in the directions of two axes which extend perpendicularly to the optical axis and to one another (X-direction and Y-direction), and in the directions of rotation about the latter axes.
The known assembly has the drawback that inevitable shrinkage in the applied adhesive as it cures may give rise to comparatively large displacements of the optical component in the Z-direction. Moreover, the likelihood of the optical component being tilted about the X and Y axes is considerable as a result of shrinkage stresses arising in the adhesive layer. The positioning problem can be reduced to some extent by making the adhesive layer thin in the Z direction, but the desired position of the optical component and the required strength and stability of the adhesive bond impose distinct restraints on this. A suitable choice of the adhesive may also reduce said problem, but wholly eliminating shrinkage and shrinkage stresses is impossible.